Messages in this thread Patch in this message | | | From | Fangrui Song <> | Date | Wed, 14 Feb 2024 14:13:01 -0800 | Subject | Re: [PATCH] x86/build: Simplify patterns for unwanted section |
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On Wed, Feb 14, 2024 at 2:07 PM Kees Cook <keescook@chromium.org> wrote: > > On Wed, Feb 14, 2024 at 01:29:29PM -0800, Fangrui Song wrote: > > A s390 patch modeling its --orphan-handling= after x86 [1] sparked my > > motivation to simplify patterns. Commit 5354e84598f2 ("x86/build: Add > > asserts for unwanted sections") added asserts that certain input > > sections must be absent or empty. The patterns can be simplified. > > > > For dynamic relocations, > > > > *(.rela.*) is sufficient to match all dynamic relocations synthesized by > > GNU ld and LLD. .rela_* is unnecessary. --emit-relocs may create .rela_* > > sections for section names prefixed with _, but they are not matched by > > linker scripts. > > > > .plt instead of .plt.* is sufficient to match synthesized PLT entries. > > Do you mean ".plt.foo" matches ".plt" ?
I mean we just need .plt : { *(.plt) } , not .plt : { *(.plt) *(.plt.*) }.
The linker synthesized section for PLT entries is .plt, not suffixed.
> > .igot and .igot.plt are for non-preemptible STT_GNU_IFUNC in GNU ld (LLD > > just uses .got), which the kernel does not use. In addition, if .igot or > > .igot.plt is ever non-empty, there will be .rela.* dynamic relocations > > leading to an assert failure anyway. > > I think at the time I was dealing with avoid multiple warnings out of > the linker, as I was getting orphan warnings in addition to the > non-empty warnings. > > > > > [1]: https://lore.kernel.org/all/20240207-s390-lld-and-orphan-warn-v1-6-8a665b3346ab@kernel.org/ > > > > Signed-off-by: Fangrui Song <maskray@google.com> > > Is anything harmed by leaving all of this as-is? > > -Kees
No harm. But ports adopting --orphan-handling= (like s390) may copy the unneeded .rela_* . When people read .rela_*, they might think whether the kernel does anything special that rela_* needs to be matched.
> > --- > > arch/x86/boot/compressed/vmlinux.lds.S | 6 +++--- > > arch/x86/kernel/vmlinux.lds.S | 8 ++++---- > > 2 files changed, 7 insertions(+), 7 deletions(-) > > > > diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S > > index 083ec6d7722a..9f288f67972a 100644 > > --- a/arch/x86/boot/compressed/vmlinux.lds.S > > +++ b/arch/x86/boot/compressed/vmlinux.lds.S > > @@ -104,17 +104,17 @@ SECTIONS > > ASSERT(SIZEOF(.got) == 0, "Unexpected GOT entries detected!") > > > > .plt : { > > - *(.plt) *(.plt.*) > > + *(.plt) > > } > > ASSERT(SIZEOF(.plt) == 0, "Unexpected run-time procedure linkages detected!") > > > > .rel.dyn : { > > - *(.rel.*) *(.rel_*) > > + *(.rel.*) > > } > > ASSERT(SIZEOF(.rel.dyn) == 0, "Unexpected run-time relocations (.rel) detected!") > > > > .rela.dyn : { > > - *(.rela.*) *(.rela_*) > > + *(.rela.*) > > } > > ASSERT(SIZEOF(.rela.dyn) == 0, "Unexpected run-time relocations (.rela) detected!") > > } > > diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S > > index a349dbfc6d5a..b3da7b81d2b3 100644 > > --- a/arch/x86/kernel/vmlinux.lds.S > > +++ b/arch/x86/kernel/vmlinux.lds.S > > @@ -463,22 +463,22 @@ SECTIONS > > * explicitly check instead of blindly discarding. > > */ > > .got : { > > - *(.got) *(.igot.*) > > + *(.got) > > } > > ASSERT(SIZEOF(.got) == 0, "Unexpected GOT entries detected!") > > > > .plt : { > > - *(.plt) *(.plt.*) *(.iplt) > > + *(.plt) > > } > > ASSERT(SIZEOF(.plt) == 0, "Unexpected run-time procedure linkages detected!") > > > > .rel.dyn : { > > - *(.rel.*) *(.rel_*) > > + *(.rel.*) > > } > > ASSERT(SIZEOF(.rel.dyn) == 0, "Unexpected run-time relocations (.rel) detected!") > > > > .rela.dyn : { > > - *(.rela.*) *(.rela_*) > > + *(.rela.*) > > } > > ASSERT(SIZEOF(.rela.dyn) == 0, "Unexpected run-time relocations (.rela) detected!") > > } > > -- > > 2.43.0.687.g38aa6559b0-goog > > > > -- > Kees Cook
-- 宋方睿
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